Abstract: A closure apparatus (1) for covering an opening (2) in a storage tank comprising: (a) a connector to connect the apparatus to the silo in the proximity of the opening (2); (b) a cover (10) to cover the opening (2), said cover having a projection (11) forming a leading edge of the cover (10), (c) an elongate guide member having a guide surface (13a, 14a), the cover (10) being slidingly engaged with the guide member and movable along the guide surface (13a, 14a) from a first position adjacent the opening (2) to a second position covering the opening (2); and (d) an actuator (4,5) to move the cover between the first position and the second position; wherein the projection (11) removes debris on the guide surface (13a, 14a) during movement between the first position and the second position.